Acquired immune deficiency syndrome (AIDS) is a very serious disease, reported cases of which have increased dramatically within the past several years. Estimates of reported cases in the very near future also continue to rise dramatically. Consequently, there is a great effort to develop drugs and vaccines to combat AIDS.
The AIDS virus was first identified in 1983. It has been known by several names and acronyms. It is the third known T-lymphocyte virus (HTLV-III), and it has the capacity to replicate within cells of the immune system, causing profound cell destruction. The AIDS virus is a retrovirus, a virus that uses reverse transcriptase during replication. This particular retrovirus is also known as lymphadenopathy-associated virus (LAV), AIDS-related virus (ARV) and, most recently, as human immunodeficiency virus (HIV). Two distinct types of HIV have been described to date, namely HIV-1 and HIV-2. The acronym HIV will be used herein to refer to HIV viruses generically.
Specifically, HIV is known to exert a profound cytopathic effect on the CD4+ helper/inducer T-cells, thereby severely compromising the immune system. HIV infection also results in neurological deterioration and, ultimately, in the death of the infected individual.
The field of viral chemotherapeutics has developed in response to the need for agents effective against retroviruses, in particular HIV. There are many ways in which an agent can exhibit anti-retroviral activity. For example, HIV requires at least four viral proteins for replication: reverse transcriptase (RT), protease (PR), transactivator protein (TAT), and regulator of virion-protein expression (REV). Accordingly, viral replication could theoretically be inhibited through inhibition of any one or all of the proteins involved in viral replication.
Anti-retroviral agents, such as AZT and ddC, are known to inhibit RT. There also exist anti-viral agents that inhibit TAT.
Nucleoside derivatives, such as AZT, are the only clinically active agents that are currently available for antiviral therapy. Although very useful, the utility of AZT and related compounds is limited by toxicity and insufficient therapeutic indices for fully adequate therapy.
Synthetic peptides also are being developed for potential use as inhibitors of the retroviral protease in the treatment of AIDS. Although these inhibitors are effective in preventing the retroviral protease from functioning, the inhibitors suffer from some distinct disadvantages. First of all, since the active site of the protease is hindered, i.e., has reduced accessibility as compared to the remainder of the protease, the ability of the inhibitors to access and bind in the active site of the protease is impaired. Secondly, the peptide inhibitors that bind to the active site of the protease are generally poorly soluble in water, causing distinct problems in drug delivery.
Therefore, new classes of antiviral agents to be used alone or in combination with AZT and/or other agents are urgently needed for effective antiviral therapy against HIV. New agents, which may be used to prevent HIV infection, are also important.